The fitting of inserts on a structure is a widespread technique for allowing equipment to be fixed to the structure. A common example is the fitting of wall plugs in a wall so as to fix an item of equipment on the wall by way of a screw engaging with the wall plug. In the field of aerospace and aeronautics, inserts are fitted in order to fix equipment to the structural panels of a satellite or aircraft. In particular, structural panels for satellites, commonly known as sandwich panels, made of composite aluminium or carbon materials having a honeycomb structure are known, said panels being employed to produce the supporting structure of the satellite or to carry solar generators. In order to allow the structure to be assembled or the equipment to be fixed, these panels are provided with numerous inserts distributed over the surface of the panel.
According to a first known technique, the insert may pass all the way through. The insert comprises for example a bolt mounted on one side of the panel and a nut on the other side of the panel. A thread formed in the bolt allows an item of equipment to be fixed to the panel. However, this technique has the drawback that the insert has a high mass.
According to a second known technique, it is possible for the insert not to pass all the way through, allowing a significant lightening of the insert. The insert can be fixed by bonding in an orifice formed in the structure. In this example, illustrated in FIGS. 1a and 1b, the insert 10 comprises a substantially cylindrical body 11 and a flange 12. In one known embodiment given by way of example, the body 11 has an outside diameter of 5 to 7 mm and the flange 12 has a diameter of 11 mm. The structure 20 is a panel consisting of an internal honeycomb structure 21 and comprising two external surfaces 22 and 23 generally made of aluminium or carbon. The insert 10 is fitted in an orifice 24 in the panel 20. The orifice 24 is configured such that, when the insert 10 butts against the end of the orifice 24, the external surface of the flange 12 of the insert is flush with the external surface 22 of the panel. The insert generally comprises a thread 13 in the body 11, said thread 13 being substantially coaxial with said body 11, allowing equipment to be fixed to the structure. The insert is secured to the panel by means of an adhesive 30 deposited in the orifice 24. For the purposes of this deposition, the insert comprises two ducts that lead into the flange 12. A first duct 15 allows adhesive to be injected into the orifice 24 and a second duct allows air present in the orifice to be evacuated. The insert is generally fitted manually. The insert is first of all deposited in the orifice. The adhesive previously prepared and placed in a syringe is then injected into the orifice through the duct 15 in the insert.
In the frequent case of a two-component adhesive, the adhesive is stored in two phases, a first phase consisting of a polymerizable resin and a second phase consisting of a hardener for initiating the polymerization of the resin after being brought into contact with the latter. Mixing the two phases is a tricky step. It is necessary to ensure good homogeneity of the mixture while avoiding the creation of air bubbles within the adhesive, said air bubbles being able to create subsequent defects in the mechanical integrity of the insert in the panel. The pot life of the adhesive is limited. The steps of mixing, integrating the adhesive in the syringe and injecting the adhesive into the insert mounted on the panel therefore have to be carried out in a very short time. In addition, the high viscosity of the adhesive complicates the handling and injection of the adhesive. Air bubbles are likely to be created during the deposition of the adhesive in the indentations of the orifice and the insert.
In order to improve production rates, attempts have been made to automate the method of fitting inserts. However, on account of these difficulties of controlling the quality of mixing and deposition, and the limited useful life of the adhesive, these automated methods remain complex and expensive and the production rates remain limited. In practice, fitting inserts remains generally manual, with small quantities of adhesive being prepared at regular intervals.
It is thus desirable to have a method for fitting inserts that makes it possible to do away with the abovementioned difficulties. In order to allow the implementation of effective automated methods, better control of the process of preparing, applying and polymerizing the adhesive is desired.